Concentration-effect relationship, definition

Other terms often used indiscriminately for the dose-response relationship include concentration-effect relationship and dose-effect relationship. According to the joint OECD/IPCS project (OECD 2003 a), which has developed internationally harmonized generic and technical terms used in chemical hazard and risk assessment, the following definitions have been provided although consensus was not achieved ... 

As no international consensus has been achieved in the OECD/IPCS project (OECD 2003a) in order to differentiate between dose (concentration)-response (effect) relationship and because it in reality is difficult to understand the subtle differences in the different terms as defined in the OECD/IPCS project, the broader and more general definition provided in the TGD (EC 2003) will be used in this book, and will generally be referred to as dose-response. Consequently, the term dose will, in this book, generally mean both dose and exposure concentration unless otherwise stated. 

Several recent reviews have concluded that, until now, no definitive cause-effect relationships have been established between exposure to environmental concentrations of chlorinated chemicals and serious adverse health consequences for humans.78-80. For fish-eating birds and mammals, however, substantial evidence... 

If the water is containing salts, these sedts cannot be carried by the vapour and therefore build up at this position. This concentration effect causes back-diffusion of salt away from the wet-dry interface. If the salts concentration near the wet-dry interface ever exceeds the solubility of the salt compounds present, precipitation is likely to occur Pi-34]. The absorption-diffusion relationship can be described by the definition of the Peclet number... 

It was found that the procedures which induced hyperglycemia without appreciably decreasing the utilization of glucose were accompanied by substantial reductions in food intake. Whether the changes are due to definite cause-and-effect relationships has not been established. The observations suggest that normally the urge to eat may be controlled by the concentration of blood glucose. 

The AEGL-1 values were based on concentrations at 0.5 ppm and 0.1 ppm, which were the thresholds for mild headaches in healthy individuals at exposure durations of 1 and 6 h, respectively (Stewart et al. 1974). This effect can be considered the threshold for mild discomfort (only one subject was affected at each exposure), which falls within the definition of an AEGL-1. The 0.5-ppm concentration was used to derive the 30-min and 1-h AEGL-1 values, and the 0.1-ppm concentration was used for the 4- and 8-h values. Because the time and concentration values were based on the most susceptible subject, these concentrations were adjusted by an uncertainty factor (UF) of 3 to account for potential differences in human sensitivity and scaled to the appropriate time periods using the C xt=k relationship. A UF of 3 was considered sufficient as no susceptible populations were identified (the headache effect is the same as that experienced by patients medicated with nitro... 

The usual definitions of maximal effect (E ) and potency EC or IC50) require another look at this stage before proceeding to developing mathemahcal relationship between drug concentration, dose, and body fxmchons using a PK/PD approach. ... 

The reaction rate expressed in terms of surface concentrations provides the relationship between Cs and CL. From the definition of the effectiveness factor, we may express the required equality of mass transfer and reaction rates as... 

Further research is required in this relatively new field to establish definitive data regarding differentiation between internal incorporation (ingestion) and external contamination (environmental), effect of hair type on analyte incorporation, time course of analyte appearance, dose vs. analyte concentration relationships, and the mechanism of drug entry into hair. Already this novel technique has proved useful in a wide variety of applications, and will unquestionably become more popular in future years. 

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